Technical Field
The present invention relates to a film for a solar cell back sheet and a method for producing the film.
Background Art
A solar cell module having crystalline silicon, amorphous silicon or the like as a solar cell element is generally produced by using a lamination method of laminating a front surface protective sheet layer, a filler layer, a solar cell element which is a photovoltaic element, a filler layer, and a rear surface protective sheet layer in this sequence, and hot pressing the laminate by vacuum suctioning. Since solar cells are placed in an environment exposed to sunlight and exposed to rain, such as on top of a roof, the respective layers constituting the solar cell module are required to have weather resistant functions such as a moisture-proof property, heat resistance and ultraviolet resistance.
The rear surface protective sheet layer is required to satisfy the conditions of, for example, having excellent strength and general robustness such as weather resistance, heat resistance, water resistance, lightfastness, wind pressure resistance, hailstorm resistance, chemical resistance, light reflectivity, light diffusibility and designability, particularly having an excellent moisture-proof property that prevents penetration of moisture, oxygen and the like, having high surface hardness, having an excellent anti-fouling property that prevents accumulation of fouling, dust and the like on the surface and very high durability, and having high protective capability.
For example, it is an aim to construct a safe solar cell module that is excellent in general properties such as a moisture-proof property, resistance to long-term performance deterioration, durability, and protective capability, at lower cost, and a rear surface protective sheet for a solar cell module has been proposed in which a heat resistant polypropylene-based resin film containing a whitening agent and an ultraviolet absorbent is laminated on both surfaces of a substrate film provided with a deposition film of an inorganic oxide (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2007-306006).
Furthermore, in addition to the functionality of the rear surface protective sheet layer itself, the productivity of the rear surface protective sheet is also an important concern, and thus there is also demand for a method for producing a rear surface protective sheet for solar cells having higher production efficiency. In general, the rear surface protective sheet for solar cells has a laminate structure including a substrate, a white layer having a sunlight-reflecting function, and various functional layers, in which the layers are mainly formed from resin films. The rear surface protective sheet is produced by affixing the respective resin films thereto.
In this regard, in order to improve the efficiency of production and fabrication of back sheets, a back sheet for solar cells has been suggested which is produced by subjecting a first resin film layer 11, a white colored layer 12, a gas barrier deposition resin film layer 13, and a second resin film layer 14 to a heat annealing treatment, and thereby imparting low shrinkability (see, for example, Japanese Patent No. 2006-073793).
A rear surface protective sheet for solar cells has also been disclosed which is formed from a substrate film, a white ink layer, and an inorganic deposit film, for the purpose of obtaining a protective sheet which has an excellent weather resistance, heat resistance, water resistance, light-fastness, wind pressure resistance, hailstorm resistance, chemical resistance, moisture proofing property, antifouling property, designability, light reflectivity, voltage resistance, and other various required properties, and has an excellent ability to reflect incident light, and which is capable of being formed and fabricated by a general-purpose method, is safe and inexpensive, and has excellent durability, so as to increase the power conversion efficiency (see, for example, Japanese Patent No. 2006-210557).